A method for constructing a life evaluation model of corrosion wear of 690 alloy heat transfer tube

Abstract

The application provides a method for constructing a life evaluation model of corrosion and wear of a 690 alloy heat transfer pipe, which is used for constructing a life evaluation model, the model considers the influence of corrosion parameters on the wear of the heat transfer pipe, the Archard model is modified, sample data of the wear of the heat transfer pipe in a specific range of corrosion parameters and mechanical parameters is accumulated through orthogonal test, and a key correction coefficient is fitted by adopting a multivariate linear regression mode, so that the wear life of the 690 alloy heat transfer pipe of a steam generator of a nuclear power plant can be more accurately predicted.

Description

Technical Field

[0001] This invention relates to the field of 690 alloy heat transfer tube wear technology, and in particular to a method for constructing a life assessment model for corrosion wear of 690 alloy heat transfer tubes. Background Technology

[0002] In a steam generator, the heat transfer tubes account for approximately 70% of the primary loop pressure boundary area, making them the weakest part of the entire primary loop pressure boundary. During long-term service, fluid vibrations or pressure fluctuations can cause fretting wear between the heat transfer tubes and the support plate, eventually thinning the tube walls and leading to failure. Currently, monitoring wall thinning primarily involves periodic inspections, replacing the tubes only when thinning reaches a certain level—a time-consuming and labor-intensive process. Therefore, developing a lifespan assessment model for heat transfer tubes to accurately predict their wear lifespan would eliminate the need for periodic inspections, saving significant manpower and resources.

[0003] Currently, the Arcard wear model is the most widely used model for predicting the lifespan of heat transfer tubes. An Arcard coefficient reflects the degree of wear between different materials; a higher coefficient indicates that the material is more prone to wear. However, real-world testing shows that the wear coefficient of a heat transfer tube is not a fixed value and is related to various factors, such as the water chemistry environment (temperature, oxygen content, and solution pH) and contact conditions. Therefore, obtaining an ideal wear coefficient through simulated real-world testing is crucial. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes, which solves the problem that the traditional Archard model is not applicable to the actual evaluation of corrosion and wear of heat transfer tubes in nuclear power plant steam generators.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes includes:

[0007] Step 1: Correct the mechanical parameters in the Archard model based on the fretting wear mechanism of the heat transfer tube;

[0008] Step 2: Introduce environmental corrosion parameters, and select different function forms to perform secondary corrections on the Archard model based on the action mechanism of each factor;

[0009] Step 3: Conduct orthogonal tests on heat transfer tube wear under different environmental corrosion parameters and mechanical parameters, obtain heat transfer tube wear volume data V under different parameter ranges, fit the data, and obtain a life assessment model for corrosion wear of 690 alloy heat transfer tube under multi-factor coupling conditions.

[0010] In step 1, the Archard model is represented by the periodic sliding motion under steady-state phase contact force, resulting in:

[0011] V M =k1FL=4nk1Fa=4k1FAft

[0012] In the formula, V M Let be the mechanical wear volume, k1 be the wear coefficient, F be the normal phase contact force, L be the relative total displacement, A be the periodic displacement amplitude, n be the number of periodic cycles, and f be the periodic displacement frequency.

[0013] In step 2, the environmental corrosion parameters include the introduction temperature, dissolved oxygen, and pH value.

[0014] Step 2 includes:

[0015] Step 2.1: Introduce contact force, displacement amplitude, and frequency correction index to perform a correction on the Archard model, and isolate the influence of each mechanical parameter to obtain:

[0016]

[0017] In the formula, k2, k3, and k4 are the contact force, displacement amplitude, and frequency correction exponent, respectively, and t is the wear time;

[0018] Step 2.2: Based on the oxide film thickness and activation energy of the Fe-Cr-Ni alloy surface, and by introducing a contact force ratio parameter, the oxide film thickness at the contact surface is obtained:

[0019]

[0020] In the formula, b1, b2, and b3 are correlation coefficients;

[0021] Step 2.3: Differentiate the wear volume of the heat transfer tube under multi-factor coupling conditions with respect to time t to obtain the wear rate expression:

[0022]

[0023] In the formula, C1, C2, C3, C4, C5, C6, and C7 are dimensionless coefficients.

[0024] In step 2.2, a corrosion chemistry model is introduced. Under high temperature and high pressure water conditions, the effects of temperature, dissolved oxygen content, and pH value are considered to obtain the formula for the thickness of the oxide film on the Fe-Cr-Ni alloy surface: h = kt. n The oxide film thickness was calculated using the formulas for Fe-Cr-Ni alloy surface oxide film thickness and the Arrhenius formula:

[0025]

[0026] In the formula, k is the chemical reaction constant, t is the chemical reaction time, n is the oxidation corrosion rate, K is the correlation constant, Q is the activation energy, T is the chemical reaction temperature, and R is the gas constant.

[0027] In step 2.2, the activation energy is:

[0028]

[0029] In the formula, Do is the dissolved oxygen content; pH is the acidity / alkalinity; and a, b, and c are dimensionless coefficients.

[0030] In step 2.3, mechanical and corrosion factors are coupled and represented by the wear volume of the heat transfer tube. The oxide film thickness on the contact surface is used as an exponential correction parameter for corrosion factors, and the following calculations are obtained:

[0031] V = V M ×dh e

[0032] The wear volume of the heat transfer tube under multi-factor coupling conditions was calculated based on the formula for the oxide film thickness of the contact surface.

[0033] In step 3, through fretting wear tests of the heat transfer tube under different operating conditions, the values ​​of each correlation coefficient are obtained using a multivariate, multi-parameter nonlinear fitting method, and the goodness of fit R is ensured. 2 Greater than or equal to 0.9.

[0034] In step 3, the mechanical parameters include displacement, frequency, and contact force.

[0035] In step 3, multiple linear regression is used for fitting.

[0036] Compared with existing technologies, the life assessment model construction method for corrosion and wear of 690 alloy heat transfer tubes provided by this invention has the following advantages:

[0037] This invention addresses the issue that the Archard model is not applicable to the actual evaluation of corrosion and wear of heat transfer tubes in nuclear power plant steam generators. Based on fretting wear tests under corrosive conditions, the Archard model is modified to achieve a more accurate prediction of the wear life of 690 alloy heat transfer tubes in power plants.

[0038] The life assessment model constructed by the method of this invention can accurately predict the wear life of 690 alloy heat transfer tubes in nuclear power plant steam generators. Detailed Implementation

[0039] The following detailed description provides further details on specific implementation methods.

[0040] This invention provides a method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes under multi-factor coupling conditions. First, the mechanical parameters in the traditional Arcard model are modified based on the fretting wear mechanism of the heat transfer tube. Then, environmental corrosion parameters such as temperature, dissolved oxygen, and pH are introduced. Different functional forms are selected according to the action mechanism of each factor to perform a secondary modification of the Arcard model, resulting in an assessment model suitable for corrosive environments. Finally, orthogonal experiments on heat transfer tube wear under different corrosion parameters (temperature, dissolved oxygen, and pH) and mechanical parameters (displacement, frequency, and contact force) are conducted to obtain heat transfer tube wear volume data V for different parameter ranges. Multiple linear regression is used for fitting, thus obtaining the life assessment model for fretting wear of 690 alloy heat transfer tubes under multi-factor coupling conditions.

[0041] This model is applicable to the fatigue life evaluation of 690 alloy heat transfer tubes under pure sliding conditions in corrosive environments (pH 8-12, dissolved oxygen 10-1000 ppb, 200-285℃) with fretting wear (displacement 10-100 μm, contact force 10-40 N, frequency 10-30 Hz).

[0042] The present invention specifically includes the following steps:

[0043] The first step is to represent the classical Archard model using the periodic sliding motion (displacement, frequency) under steady-state phase contact force, as shown in equation (1).

[0044] V M =k1FL=4nk1FA=4k1FAft (1)

[0045] In the formula, V M Let be the mechanical wear volume, k1 be the wear coefficient, F be the normal phase contact force, L be the relative total displacement, A be the periodic displacement amplitude, n be the number of periodic cycles, and f be the periodic displacement frequency.

[0046] The second step is to introduce contact force, displacement amplitude, and frequency correction index to make a correction to the Archard model and remove the influence of each mechanical parameter, as shown in equation (2).

[0047]

[0048] In the formula, k2, k3, and k4 are the contact force, displacement amplitude, and frequency correction index, respectively, and t is the wear time.

[0049] The third step is to introduce a corrosion chemistry model. Under the influence of factors such as temperature, dissolved oxygen content and pH value, the change of the oxide film thickness on the Fe-Cr-Ni alloy surface with time can be represented by equation (3). Then, considering the Arrhenius formula (4), equation (5) is obtained.

[0050] h = kt n (3)

[0051]

[0052]

[0053] In the formula, h is the oxide film thickness; k is the chemical reaction constant; t is the chemical reaction time; n is the oxidation corrosion rate; K is the correlation constant; Q is the activation energy; T is the chemical reaction temperature; and R is the gas constant.

[0054] The activation energy in equation (5) is expressed in terms of dissolved oxygen content and pH value, as shown in equation (6).

[0055]

[0056] In the formula, Do represents dissolved oxygen content; pH represents acidity / alkalinity; and a, b, and c are dimensionless coefficients. Because the Do value varies greatly under experimental conditions, a logarithmic calculation is required. Acidity / alkalinity is based on a pH of 7.

[0057] Substituting equation (6) into equation (5) and combining the relevant parameters, we consider that the chemical reaction time is related to the displacement frequency of fretting wear. Furthermore, for pipe-plane contact, since high-temperature water has difficulty entering the contact gap, the oxidation of the friction pair surface is hindered. The greater the contact force, the greater this hindering effect. Therefore, a contact force proportionality parameter needs to be introduced to reflect this phenomenon. Then, the growth law of the oxide film thickness on the contact surface can be expressed by equation (7).

[0058]

[0059] In the formula, b1, b2, and b3 are dimensionless coefficients.

[0060] The fourth step is to couple the mechanical and corrosion factors and represent them with the wear volume of the heat transfer tube. The oxide film thickness of the contact surface is used as an index correction parameter of the corrosion factor and added to the mechanical wear volume calculation formula shown in equation (2) to obtain the expression of wear volume V in equation (8).

[0061] V = V M ×dh e (8)

[0062] Substituting equations (2) and (7) into equation (8) and combining the correlation coefficients, we can obtain the wear volume of the heat transfer tube under multi-factor coupling conditions. After differentiating with respect to time t, we obtain the wear rate expression, as shown in equation (9).

[0063]

[0064] In the formula, C1, C2, C3, C4, C5, C6, and C7 are dimensionless coefficients.

[0065] The fifth step involves conducting fretting wear tests on the heat transfer tubes under different operating conditions. A multivariate, multi-parameter nonlinear fitting method is used to determine the values ​​of each correlation coefficient, ensuring the goodness of fit R0. 2 Greater than or equal to 0.9. Since the test was carried out within a specific range of corrosion and mechanical parameters, the life assessment model for fretting wear of 690 alloy heat transfer tubes under multi-factor coupling conditions is applicable in the following ranges: pH 8–12, dissolved oxygen 10–1000 ppb, 200–285℃; displacement 10–100 μm, contact force 10–40 N, and frequency 10–30 Hz.

[0066] Therefore, this invention conducts orthogonal tests on the fretting wear of 690 alloy heat transfer tubes under corrosive environments to obtain key wear data within different ranges of mechanical parameters (displacement, frequency, contact force) and corrosion parameters (temperature, oxygen content, and solution pH). The original Archard model is then modified to construct a heat transfer tube wear life assessment model under corrosive environments, so as to achieve the goal of more accurately predicting the fretting wear life of heat transfer tubes.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes, characterized in that, include: Step 1: Correct the mechanical parameters in the Archard model based on the fretting wear mechanism of the heat transfer tube; Expressing the Arcard model in terms of periodic slip motion under stable phase contact force, we obtain: In the formula, V M For mechanical wear volume, k 1 The wear coefficient is... F For the contact force of the Dharma phase, L This represents the relative total displacement. A The periodic displacement amplitude, n The number of cycles. f The periodic displacement frequency; Step 2: Introduce environmental corrosion parameters and perform secondary corrections to the Archard model by selecting different function forms based on the mechanism of action of each factor; Step 2 includes: Step 2.1: Introduce contact force, displacement amplitude, and frequency correction index to perform a correction on the Archard model, and isolate the influence of each mechanical parameter to obtain: In the formula, k 2. k 3. k 4 represents the contact force, displacement amplitude, and frequency correction index, respectively. t Wear time; Step 2.2: Based on the oxide film thickness and activation energy of the Fe-Cr-Ni alloy surface, and by introducing a contact force ratio parameter, the oxide film thickness at the contact surface is obtained: In the formula, b1, b2, and b3 are dimensionless coefficients; Step 2.3: Obtain the wear volume of the heat transfer tube versus time under multi-factor coupling conditions. t After differentiation, the wear rate expression is obtained: In the formula, C1, C2, C3, C4, C5, C6, and C7 are dimensionless coefficients; In step 2.3, mechanical and corrosion factors are coupled and represented by the wear volume of the heat transfer tube. The oxide film thickness on the contact surface is used as an exponential correction parameter for corrosion factors, and the following calculations are obtained: The wear volume of the heat transfer tube under multi-factor coupling conditions was calculated based on the formula for the oxide film thickness of the contact surface. Step 3: Conduct orthogonal tests on heat transfer tube wear under different environmental corrosion and mechanical parameters to obtain wear volume data of heat transfer tubes within different parameter ranges. By fitting the data, a life assessment model for corrosion and wear of 690 alloy heat transfer tubes under multi-factor coupling conditions was obtained.

2. The method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes according to claim 1, characterized in that, In step 2, the environmental corrosion parameters include the introduction temperature, dissolved oxygen, and pH value.

3. The method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes according to claim 1, characterized in that, In step 2.2, a corrosion chemistry model is introduced to derive the formula for the oxide film thickness on the Fe-Cr-Ni alloy surface under the influence of temperature, dissolved oxygen content, and pH value in a high-temperature, high-pressure water environment. The oxide film thickness was calculated using the formulas for Fe-Cr-Ni alloy surface oxide film thickness and the Arrhenius formula: In the formula, k It is a chemical reaction constant. t For chemical reaction time, n Where is the oxidation corrosion rate, K is the correlation constant, Q is the activation energy, T is the chemical reaction temperature, and R is the gas constant.

4. The method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes according to claim 1, characterized in that, In step 2.2, the activation energy is: In the formula, Do is the dissolved oxygen content; pH is the acidity / alkalinity; and a, b, and c are dimensionless coefficients.

5. The method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes according to claim 1, characterized in that, In step 3, through fretting wear tests of the heat transfer tube under different operating conditions, the values ​​of each correlation coefficient are obtained using a multivariate, multi-parameter nonlinear fitting method, and the goodness of fit R is ensured. 2 Greater than or equal to 0.

9.

6. The method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes according to claim 1, characterized in that, In step 3, the mechanical parameters include displacement, frequency, and contact force.

7. The method for constructing a life assessment model for corrosion and wear of 690 alloy heat transfer tubes according to claim 1, characterized in that, In step 3, multiple linear regression is used for fitting.

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